‘11 35i coolant boiling over

[Scott_S]

I just replaced a leaking water pump/thermostat with OE parts and coolant. It has been fine for about a month, but twice in the last week when driving a few miles in town the coolant is boiling out of the reservoir. It has been fine on longer drives and on the highway. I’ve verified the water pump is running, the fan kicks on, but not sure it’s running all the time? The tank and cap are only about a year and a half old.
I was thinking maybe it’s the cap, but I am looking for any input on where to look.

[dang2407]

I'd start by looking at the water temp either on the hidden dash option or a phone app. It might give a clue as to what and when is happening...

[Poppyboy]

The symptoms point to improper bleeding, but if there was an air bubble, you’d think things wouldn’t be fine for a month. I would go the inexpensive route by draining and using a coolant vacuum fill tool.

[Scott_S]

Originally Posted by dang2407

I'd start by looking at the water temp either on the hidden dash option or a phone app. It might give a clue as to what and when is happening...

How do you get to the dash option?

[Scott_S]

Originally Posted by Poppyboy

The symptoms point to improper bleeding, but if there was an air bubble, youÂ’d think things wouldnÂ’t be fine for a month. I would go the inexpensive route by draining and using a coolant vacuum fill tool.

That was my original thought, but I would think it would happen all of the time driving and not just when we drove around town. My next thought was that the fan might have an issue, which would help explain why it is ok on the highway when there is proper air flow, but I did see the fan turn on for a short period while inspecting it yesterday so I know that it is at least operational.

[dang2407]

Originally Posted by Scott_S

How do you get to the dash option?

Something to do with holding down the odometer reset button. It doesnt work for me so I have an OBD2 adapter plus phone app. Adapter is about €10 and free apps like OBD Facile give access to the basic measures such as water temp.

[jcattletown]

Originally Posted by Scott_S

How do you get to the dash option?

when engine is running, push and hold the odometer reset knob until you see the center section of the dashboard reveals the hidden menu. Release the knob, then keep pushing the knob to go to the unlock menu (I believe it is 19) and enter the sum of your last 5 digit VIN# to unlock information. Then keep pushing the knob until it hits 7 and stop. The water temperature will be displayed as celsius.

[Scott_S]

Sorry for the delay, it’s been busy. I have verified that the fan is working properly and the water pump is a new VDO(I think that is a BMW OEM?) and it seems to run as expected. I did see that the reservoir cap had a small chip in it that allowed the lower o-ring to slip off, so I replaced that with an OE unit.
The issue is still happening as of today, I ran the vehicle with the cap off and watched the fan kick on. Once it got up to temp I noticed that the stream coming into the reservoir stopped sometimes, I am not sure if that is normal or if that is indicative of air in the system. Also a few times I saw the coolant level rise way up and run over before going back down.

The only thing I can think of is I need to try and bleed the system again. Any other ideas that I am missing? This is getting really annoying.

[My135i]

I opened up the expansion tank from cold start and start it then turn on heater full hot, then you'll see your coolant will have bubbles if you have air then eventually will stop the bubbles and when coolant starts to come up, i put the cover back...